They don't really work. They just are. Or maybe they're a general indication of something. I don't think any of us are clear on the subject.
Actually, some people like feedback, hence a system built into the forum software is used to allow for such things. It used to be anonymous, which drove lots of people crazy when they couldn't figure out why they were lauded or dissed. Now at least the person giving or taking one has to say a few words and identify themselves.
It's for fun mostly. Don't count on them or give them much credence. I've spent a hour writing some long response to a ditzy theist and gotten nothing one day and then told a fart joke the next day and gotten two Darwins. There is no rhyme nor reason.
Edit: Looks like I completely misunderstood the question. That gets me in trouble a lot. Hope the others answered it for you.